1. Field of the Invention
This invention relates to a composition and method for making a silicone article that has a textured non-blocking surface.
2. Prior Art
As is well known in the art, silicone articles may be formed by dipping or otherwise depositing a dispersion of silicone on an appropriate form. The dispersion may also contain a vulcanizing agent along with accelerators and other additives. After each layer of dispersion is deposited on the form, the layer is permitted to cure and the process is repeated until the outer shell of the article reaches the required thickness.
A smooth untreated elastomer surface has the physical characteristic of blocking; that is, the characteristic of sticking to itself and other surfaces. For some applications blocking is undesirable. For example, blocking is undesirable in latex, silicone and other elastomer gloves because it makes them difficult to don. Various lubricants and release agents have been dusted or otherwise applied to gloves to improve performance and overcome blocking. The shedding of these lubricants can cause undesirable side-effects, such as contamination, infection and foreign body reactions due to powders from gloves entering the wound during surgical procedures. As a result, much of the early work on textured surfaces was performed on latex surgical gloves. U.S. Pat. No. 3,761,965, discloses a sanitary glove having a textured surface provided by a granular vinyl chloride polymer imbedded on the surface of the film from which the glove is manufactured. This glove is suitable for donning without the use of a lubricant such as powder. However, this type of glove has the same type of problem as talc-dusted gloves in that particulates may enter a wound causing an adverse foreign body reaction. Dusted gloves are, therefore, not generally suitable for surgical procedures.
U.S. Pat. No. 1,983,963 discloses a method of providing a textured surface on a rubber glove which subjects the vulcanized surface of the glove to the action of a rubber solvent or swelling agent such as naphtha, benzol or gasoline either by immersion or by subjecting the surfaces to the fumes of these chemicals. This process, which is similar to etching, has not enjoyed widespread use and is not adaptable to silicone.
U.S. Pat. No. 4,143,109, issued to Stockum, describes a method of dip-coating a first layer of natural rubber latex onto a glove form, the form having the general contour of a human hand, followed by dip-coating a second layer containing particulates which are randomly distributed throughout the dispersion. After curing, the glove is inverted and may be donned without the use of lubricants. The general method developed by Stockum for latex articles has not been transferable to silicone articles because the particulates taught by Stockum for use with latex would weaken the outermost layers of silicone substantially.
The foregoing inventions have been developed for latex articles. U.S. Pat. No. 4,061,709 to Miller, et al, describes a method for manufacturing silicone rubber gloves with a non-blocking surface by repeatedly dipping a form in a solvent dispersion of uncured silicone rubber to build up a plurality of layers and then forming a layer of liquid droplets on the surface of the article thereby forming an irregular or textured surface as the solvent evaporates. Utilization of this method for physically altering the exterior uniformly from lot to lot requires a highly controlled manufacturing environment which is difficult and expensive to maintain. The present invention utilizes a unique dispersion which produces a uniformly textured non-blocking surface.
There are other areas where a non-organic, non-contaminating, non-blocking, non-allergenic, texturized surface with low reflectivity and high diffusivity would be highly advantageous. Some space applications demand low reflectivity or high diffusivity in paints and coatings. Epoxies, and almost all organic coatings other than silicone, are not durable enough to withstand the highly oxidizing atmospheres that satellites must endure. For example, an anti-blocking silicone surface is necessary in a bellows or in a rolled solar array to facilitate separation of adjacent surfaces during deployment. Until now, prior art silicone technology has not been able to produce contaminant-free silicone anti-blocking, low-reflectivity, high diffusivity outer layers which are sufficiently durable to withstand the physical and chemical properties of these extreme environments.